1. Field of the Invention
This invention generally relates to drop-on-demand ink jet printers and, more particularly, with the method of manufacturing a component of the ink propulsion system. The term "ink jet" as used herein is intended to include all drop-on-demand ink propulsion systems including, but not limited to, "bubble jet,""thermal ink jet" and piezoelectric.
2. Description of the Prior Art
The basic concept of ink jet printing is described in U.S. Pat. No. 4,490,728 entitled "Thermal Ink Jet Printer" issued Dec. 25, 1984 to Vaught et al.
The general construction of a thermal ink jet print head is described in U.S. Pat. No. 4,683,481 entitled "Thermal Ink Jet Common-Slotted Ink Feed Printhead" issued Jul. 28, 1987 to Johnson.
The general arrangement of thermal ink jet barriers, nozzle plates, resistors, and ink flow paths is disclosed in U.S. Pat. No. 4,882,595 entitled "Hydraulically Tuned Channel Architecture" issued Nov. 21, 1989 to Trueba et al.
These patents disclose a print head having an ink containing capillary with an orifice for ejecting ink and an ink heating mechanism, generally a resistor, in close proximity to the orifice. In operation, the ink heating mechanism is quickly heated, transferring a significant amount of energy to the ink, thereby vaporizing a small portion of the ink and producing a bubble in the capillary. The bubble in turn creates a pressure wave which propels an ink droplet or droplets from the orifice onto a nearby writing surface. By controlling the energy transfer to the ink, the bubble quickly collapses before it can escape from the orifice.
There are two problems due to the ink which arise with respect to the barriers which define the ink channels within printheads. The first problem is that the ink chemically attacks the barrier and causes either leakage between the channels and/or leakage to the outside of the pen and also causes swelling of the barriers. Swelling results in a change in channel geometry and a degradation from optimized performance. The problem of chemical attack is especially important with the newly developed inks having pH's in excess of 9 and highly penetrating cosolvents. The second problem is adhesion of the orifice plate. In most applications the orifice plate has a nickel surface and is bonded to the print head using a combination of heat and pressure. If the ink attacks the ink channels, it can destroy the adhesion of the orifice plate and cause delamination or separation of the orifice plate from the print head.
The use of hardened photosensitive resins to form barrier walls is generally disclosed in U.S. Pat. No. 4,417,251 entitled "Ink Jet Head" issued Nov. 22, 1983 to Sugitani and U.S. Pat. No. 4,558,333 entitled "Liquid Jet Recording Head" issued Dec. 10, 1985 to Sugitani et al.
There is a further problem of selecting appropriate materials for the fabrication of barriers. Barriers are produced today from negatively acting, photoimageable material. These materials have been used for many years in the manufacture of both printed circuit boards and integrated circuits. However, a typical photoimageable material that is used for printed circuit boards can resolve 8 mil (203.2 microns) traces and 8 mil (203.2 micron) spaces. In addition, typical materials used in integrated circuits have a resolution of 1 micron traces and 1 micron spaces. In contrast, the present invention requires resolution for approximately 20 micron traces and 20 micron spaces which is in between the typical specifications for printed circuit board and integrated circuits.
In other words, the materials commonly used in the manufacture of printed circuit boards can not be used in the present invention because these materials do not provide the high order of resolution that is required. If these materials are used to fabricate barriers, the resulting barriers are rough and granular. These are defects which cause unwanted flow discontinuities, obstructions and turbulence within the ink channels.
Likewise the materials commonly used for integrated circuits are unusable because they are optimized to resolve dimensions on the order of 1 micron. When used to fabricate barriers having dimensions of approximately 25 microns, most integrated circuit materials lose all resolution. The material to be removed from the channels becomes too polymerized and can not be removed by conventional techniques.
The foregoing status of the art thus indicates that a need has existed in this field for a barrier segment material which can withstand the corrosion of high pH inks, stop delamination of the orifice plate, and also provide the required ink channel resolution.